A dental implant is implanted in a jawbone in order to substitute a function of a lost tooth therewith, and Patent Literature Document 1 discloses such a screw type dental implant in which a screw part formed of a spiral protrusion to be implanted in an alveolar bone, is formed. And, in a dental implant operation, it is important that the dental implant is fully combined with the bone (Osseointegration), so that in the Patent Literature Document 1, it is proposed that organic matters are removed by irradiating the dental implant with ultraviolet rays.
It is desired that in a light irradiation device, which irradiates such a dental implant with ultraviolet rays, the screw part which is implanted in the alveolar bone etc., be certainly irradiated with ultraviolet rays, and further two or more dental implants be simultaneously irradiated with ultraviolet rays since in one dental implant operation, the two or more dental implants are usually used. However, a light irradiation device, which suitably irradiates the two or more screw type dental implants with ultraviolet rays, was not known.